The present invention relates to a method of and an apparatus for finishing the perforated holes in cigarette filter tipping paper, and more particularly to a method of and apparatus for abrasively removing the flaps formed adjacent the perforated holes during a mechanical perforation process.
One method of reducing the "tar" and nicotine delivery of a cigarette is through the use of air dilution. In order to produce air dilution, minute holes or perforations are formed in the cigarette filter tipping paper which allow air to be drawn laterally into the cigarette filter and combined with the tobacco smoke. One conventional method of forming the perforations is to mechanically perforate the filter tipping paper prior to forming the cigarette filter. Typically, the perforations are not punched completely clean, but rather small flaps of paper or paper fibers from the perforations remain affixed to the tipping paper adjacent each such perforation.
Throughout the specification and claims herein, the term "flap" is generally intended to describe those remnants of paper or paper fibers which remain adhered to the periphery of a mechanically perforated hole in a paper web as a result of a mechanical perforation process. In such a mechanical perforation operation for perforating a web of cigarette filter tipping paper, the perforations are typically formed in the web in a pair of spaced, longitudinally extending series of holes disposed closely adjacent to one another. Normally, a flap remains connected to the periphery of a perforation at the leading edge thereof.
During manufacture of the cigarette filter, some of the flaps are inadvertently "raked" back by the processing machinery, thus blocking the perforations associated with the flaps. The number of flaps raked back over the perforations varies widely, resulting in variations of air dilution and unpredictable "tar" and nicotine levels. Thus, there has been a need in the art for a simple and dependable method of and apparatus for removing the flaps from the tipping paper after holes have been mechanically perforated therein.
A search of the prior art failed to uncover any prior art references which disclose apparatus that would be suitable for accomplishing the required flap removal operation. One prior art reference, U.S. Pat. No. 2,801,501, discloses an apparatus for perforating tea bag paper wherein the paper is interposed between an embossing drum and two sanding belts which pass in opposite directions over diametrically opposed portions of the drum. One sanding belt is passed over the paper and drum in a direction opposite paper and drum rotation to abrade and perforate the paper against the embossments on the drum and the second belt travels in the same direction as the paper and drum rotation to buff off burrs on the paper web. One drawback of the prior art apparatus is that perforation and burr removal are performed on the same drum so that the projections on the embossing drum are abraded as well as the paper burrs, resulting in excessive wear of the drum. In addition, removal of the burrs is rendered more difficult and inefficient because the paper is not compressed between contiguous surfaces with a uniform pressure.
U.S. Pat. No. 3,435,566 discloses a method of deburring holes in a flat metal workpiece comprising conveying individual workpieces against a grinding wheel rotating at high speed relative to the speed of the workpiece and in the same direction in which the workpiece is conveyed. The method disclosed in that patent is not suitable for use on a continuous web of thin, flexible paper because the method relies on only a line contact between the workpiece and grinding wheel and there is no satisfactory means for controlling the pressure on a flexible paper workpiece. In addition, the very high relative speed between the grinding wheel and the workpiece would tend to destroy or damage a thin filter paper web.